GWL methods consist in measuring a certain value characterizing one or more physical properties of rocks along a borehole in pressure-temperature conditions that are determined by the rock's depth and different geological and technological conditions.
Currently more than 50 GWL methods and their variations are known. A disadvantage of known methods is that the measurement of physical values of rocks at certain depths is performed at certain pressure-temperature conditions that remain unchanged during logging.
Determination of properties of rocks determination during by varying formation temperature is known from prior art methods. Thus, USSR Certificate of Authorship No. 1125519 describes a method for determining formation properties according to which a deposit is heated and a nuclear magnetic resonance (NMR) logging measurement or acoustic logging measurement is performed before the deposit is heated and after the deposit is heated. A free fluid index, a spin-lattice relaxation and a porosity are measured. Based on these values, an oil recovery factor is estimated. The heating is performed by injecting a heating agent or by means of fireflooding.
The closest prior art is a method for determining parameters of a formation as described in U.S. Pat. No. 6,755,246, wherein active or passive heating of the formation is performed to increase a temperature of fluids in the formation thus changing a relaxation time T2 of NMR spin echo measurement which is used to identify and quantify heavy oil saturation. This method's disadvantage is that it is performed by “logging-exposure-logging” which significantly increases the GWL time.
Another disadvantage of the NMR logging method is that decay times are so short in some formations, for example, in tight sands, that signals cannot be measured. The main problem with relating NMR relaxation times to formation permeability is that pores probed by NMR are not necessarily hydraulically connected. Consequently, an impermeable medium containing disconnected vugs may yield the same T1 decay curves as a permeable rock containing connected pores.